1. Field of the Invention
The present invention relates to an optical fiber and to a transmission path that uses the optical fiber.
2. Description of the Related Art
Corresponding to increases in the volume of data traffic, increases in the transmission capacity of networks are required.
For example, wavelength division multiplexing (WDM) system is a transmission system which is designed to meet this requirement and is already available commercially.
Moreover, in recent years, investigations have been made into using WDM transmissions not only in long haul systems, but also in metro and access systems.
WDM transmission systems, which are considered applicable to a metro and access system, can be broadly categorized into two types. One type is known as dense WDM (DWDM). This type is almost the same as long haul systems.
The other type is known as coarse WDM (CWDM). This type is a method that spreads each signal wavelength interval uses wide wavelength band.
In WDM transmissions over a relatively short distance (distances up to approximately 200 km may be included in the definition “relatively short distance”), such as in the case with a metro or access system, the system cost is extremely important factor to design the system. As a result, it is necessary for the optical fiber used in such a transmission path to be low in price.
In the case of the installation of optical fiber to private homes and offices (Fiber to the Home—FTTH), in addition to low price, there is another requirement which is required to the fiber for the above described WDM transmission path. Namely, when a fiber is laid in a building or private home, there is a possibility that the optical fiber will be conditioned under extremely small bending of the order of 30 φmm or 20 φmm.
Furthermore, it is extremely important that there is no loss increase even if the fiber is coiled in a small bending diameter in order to store surplus fiber. Therefore, the fiber to the FTTH should be tolerant to the bend.
In contrast, conventionally, several types of optical fiber have been proposed that are suitable for WDM. However, all of them have, for example, three or more layers of complicated refractive index profile and are expensive because of such complicated structure.
Moreover, conventional 1.3 μm band single mode fibers or multimode fibers are generally used in offices and homes, conventionally. However, these fibers generally only tolerate a bending diameter of approximately 60 mm. Consequently, when the fiber is being laid out careful attention is needed to ensure that there is no excessive bending. Recently, fibers have become commercially available those are based on ITU-T G. 652, which is an international standard for 1.3 μm band single mode fibers, and tolerate a bending diameter of 30 mm by reducing the size of the mode field diameter (MFD). However, the additional development is awaited of an optical fiber that can cope with still smaller bending diameters for wiring in buildings and private homes.
The present invention was conceived in view of the above circumstances and it is an object thereof to provide a low price optical fiber that is suitable for WDM transmission.
A second object is to provide an optical fiber capable of being laid with a small bending diameter or of allowing surplus fiber thereof to be stored in small diameter.